The sizes of the loads transported by railroad cars can vary widely. By way of example, although they are often loaded with up to several tons of goods or material, they are also sometimes transported empty after the loads have been delivered. For this reason, and since the amount of braking force required to stop a railroad car is dependant upon the size of the load being transported, railroad cars typically include load weight sensors. The load weight sensors provide information representative of the car load to the brake system, thereby enabling the brake system to apply braking forces appropriate for the load being transported.
Pneumatic (i.e., air actuated) brake systems are widely used on railroad cars. The load weight sensors commonly incorporated into these systems are mechanically actuated valves for regulating the amount of air applied to the brakes as a function of the measured load. The valves are mounted across the suspension springs between the car body and wheels, and effectively regulate the brake air flow as a function of the compression of the suspension springs (e.g., the greater the weight the more the more the springs are compressed and the valve opened to allow greater air flow to the brakes). These mechanical load weight sensors are, however, relatively expensive to maintain.
Ultrasonic systems for monitoring railroad car loads have also been developed. These systems were mounted to the outside of the car and measure suspension spring compression (e.g., load) by monitoring the distance between the car body and the railroad track or ground. Unfortunately, the accuracy of these ultrasonic systems can be less than desirable since a relatively wide ultrasonic beam is required to make the systems operable over a range of railroad car speeds and directions. Noise generated by the wheels on the rails can also interfere with the operation of the systems. They are also susceptible to damage from debris.
It is evident that there is a continuing need for improved load weight sensors for use in rail car applications. To be commercially viable the system should be accurate and efficient to manufacture and maintain. A system of this type would be especially desirable if it were capable of being interfaced to the electronic air brake systems (EABS), also known as electronically controlled pneumatic (ECP) brake systems, being incorporated into railroad cars.